by Michael Smith Michael Smith North American Correspondent, MedPage Today
March 12, 2015

Action Points

A post-Ebola measles outbreak with deaths rivaling those from Ebola could occur due to Ebola-related interruptions in healthcare systems.

Emergency measles vaccination campaigns could avert much of the estimated post-Ebola measles cases.

The death toll from post-Ebola measles outbreaks in three West African countries could rival that of Ebola itself, researchers are warning.

The finding, based on mathematical modeling, assumes that the Ebola epidemic will last a total of 18 months, during which measles vaccination rates will be reduced by 75% of what they were when it started, according to Justin Lessler, PhD, of Johns Hopkins Bloomberg School of Public Health.

If that's the case, an estimated 1.129 million children would be unvaccinated in Guinea, Liberia, and Sierra Leone -- about 400,000 more than had their shots when the Ebola outbreak began, Lessler and colleagues reported in the March 13 issue of Science.

A generalized measles outbreak in the region could then lead to as many 227,000 cases and between 2,000 and 16,000 deaths, Lessler told reporters in a telebriefing on the research.

The numbers "sound pretty bad, but they are not unprecedented," Lessler said: An outbreak in the Democratic Republic of the Congo in 2010 through 2013 caused 294,000 cases and more than 5,000 deaths.

By comparison, while the Ebola epidemic is still not over, the number of fatalities up to March 8 is 9,961, according to World Health Organization data.

All three countries, where reported measles vaccination rates in 2013 ranged 62% to 83%, had been planning immunization drives when the Ebola crisis erupted, Lessler told reporters.

But those were disrupted along with most other non-Ebola medical services, Lessler said.

The disruption in medical systems could lead to a "second infectious disease crisis that could kill as many as, if not more than the original (Ebola) outbreak," he and colleagues wrote in Science.

Lessler told reporters one aspect of the analysis -- the assumption that vaccination has been at 25% of pre-Ebola rates -- might be "a touch too pessimistic" based on recent information.

"But even our least pessimistic scenario of a 25% reduction in vaccination rates would be expected to result in tens of thousands of additional cases and between 500 and 4,000 additional deaths," he said.

In its midweek report Wednesday, the WHO said the three countries have now recorded 24,247 confirmed, probable, and suspected cases after about 15 months of the Ebola epidemic, which began in December 2013.

For the second week in a row, Liberia has reported no new cases and has no patients under care. In the first 4 days of March, Liberian healthcare workers tested 90 people suspected of having Ebola and none was positive for the virus. Some 102 contacts were being followed up, the agency said.

On the other hand, Guinea and Sierra Leone each reported 58 cases, mostly clustered in and around their respective capitals, Conakry and Freetown.

The smaller geographic range of the new cases is cause for optimism, the WHO said, since it means the epidemic response can be more focused.

But the agency cautioned that the number of Ebola deaths occurring in the community rather than in treatment centers suggests there are still "significant challenges in terms of contact tracing and community engagement."

In Guinea, 24 of the 40 confirmed Ebola deaths in the week ending March 8 were in the community, the WHO reported, compared with 11 of 83 in Sierra Leone.

As well, only 14% of the confirmed Ebola cases reported from Guinea arose among known contacts of previous cases, suggesting that there are unknown chains of transmission and that -- even in known transmission chains -- not all contacts are being traced.

Sierra Leone appears to be doing slightly better on that front, the agency reported -- over the same period, 64% of confirmed cases arose among known contacts.

The bright side of the measles story, Lessler told reporters, is that it might be possible to avert any outbreak by beginning emergency vaccination campaigns as soon as possible.

"The solution is clear," he said. "Supplemental immunization campaigns have been conducted in all three countries in the past and could virtually eliminate Ebola's effect in the region."

Such campaigns should also target a range of other diseases, such as polio, diphtheria, and tuberculosis, added Saki Takahashi, a doctoral student from Princeton University, who was the paper's first author.

Measles outbreaks often follow humanitarian crises for two reasons, the researchers noted: the virus itself is highly contagious and vaccination rates tend to be lower in the first place.

To estimate the effect of the Ebola crisis, the researchers used data from demographic and health surveys in the region to map the locations of unvaccinated children.

They combined that data with information on population and birth cohort size to get a picture of how many children, 9 months to 5 years, were unvaccinated before the Ebola-driven disruption of the healthcare systems.

Their primary analysis was conducted assuming a 75% reduction in vaccination rates, but they also performed sensitivity analyses assuming reductions of 25%, 50% and 100%.

At the start of the Ebola outbreak, they estimated that 778,000 unvaccinated children were living in a large contiguous cluster that included parts of all three countries. Assuming the 75% reduction in vaccination rates, each month of healthcare disruptions would increase the number of unvaccinated children by 19,514 on average.

After 18 months, the population of unvaccinated children would have almost doubled, to 1.129 million, they estimated.

If vaccination had continued at pre-Ebola rates, they reported, a generalized measles outbreak could have caused about 127,000 cases. But the addition of so many unvaccinated children suggests an outbreak after 18 months of the Ebola crisis could cause as many as 227,484 cases, they argued.

The study had support from the Bill and Melinda Gates Foundation, the Department of Homeland Security Science and Technology Directorate, the NIH, and the NIAID. The authors made no disclosures.

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